The present invention relates to a liquid separator, and more particularly to an apparatus for separating various blood portions or components such a blood plasma, red cells, etc. from blood stored in a flexible container such as a blood bag or the like.
It is known that conventional whole blood transfusion causes various problems particularly with respect to patients to whom blood is transfused. To avoid physical strains on the body of patients and reduce harmful immunity-related side effects, there has generally been employed component transfusion by which only a blood component required by a patient is transfused to the patient. Component preparations can be produced by separating, with a centrifugal separator, various blood components from blood stored in a blood bag, and storing the separated blood components in respective component bags.
Various devices are known for separating blood in a blood bag into blood components. These separating devices are roughly divided into two groups. According to a separating device of one group, the blood bag is locally pressed in its lower portion. A separating device of the other type presses the blood bag uniformly over its entire area.
The former blood separator is disclosed in Japanese Patent Publications Nos. 55-17585, 57-30507, and 62-502594, for example. The disclosed blood separator includes a separating stand 2a as shown FIG. 1(a) of the accompanying drawings.
Blood contained in a blood bag 4a is separated into blood components by a centrifugal separator One of the separated components, i.e., blood plasma, is then separated into a component bag (not shown) by the separating stand 2a, and thereafter, a tube 6a extending between the blood bag 4a and the component bag is sealed off by a tube sealer (not shown).
More specifically, the blood bag 4a is hung from a hook 7a on the separating stand 2a such that red cells in the blood bag 4a will not be agitated and mixed with the other separated blood components. Then, the blood bag 4a is pressed by a presser plate 9a that is angularly moved about a pivot shaft 8 in the direction indicated by the arrow A. Since the presser plate 9a is rotatably mounted on the separating stand 2a by the pivot shaft 8 that is positioned below the blood bag 4a, the lower portion of the blood bag 4a is compressed to force blood plasma out of the blood bag 4a upwardly into the component bag through the tube 6a joined to the upper end of the blood bag 4a. By continuously pressing the blood bag 4a until the interface between the blood plasma and the red cells reaches the upper end of the blood bag 4a. After the blood plasma has entirely been separated from the blood bag 4a, the tube 6a is sealed off by the tube sealer.
The latter blood separating device is known from Japanese Laid-Open Patent Publications Nos. 55-155652 and 61-29363, for example. The blood separating device employs a separating stand 2b as illustrated in FIG. 1(b) of the accompanying drawings. In operation, a blood bag 4b is hung from a hook 7b on the separating stand 2b with care exercised not to disturb separated red cells in the blood bag 4b. Then, the blood bag 4b is uniformly compressed by a presser plate 9b which is horizontally displaced toward the separating stand 2b in the direction indicated by the arrow B. Blood plasma is forced out of the blood bag 2b into a component bag (not shown) through a tube 6b.
The blood separators of the above two types may be operated either automatically or manually. If they are operated automatically, the interface between the blood plasma and the red cells in the blood bag is automatically detected by an optical interface sensor.
With the conventional blood separators, however, since the interfacial areas S.sub.1, S.sub.2 between the blood plasma and the red cells or a buffy coat layer in the blood bags 2a, 2b are large, any error in the detection of the interfacial position by visual inspection or the optical interface sensor induces a large error in the amount of the separated component. Accordingly, the desired blood component may not be separated with a good yield.